Week 1 Walk in the Cold The eighteenth-century walker and writer Elizabeth Carter claimed her favorite walks were those taken in "whistling winds and driving snows." Carter wasn''t as unusual as we might think. Over the years, hundreds of walkers have expressed an enduring love for ice-blasted walks in the glacial depths of winter. In Christiane Ritter''s astounding account of living in the Arctic Circle, she describes her daily walk in temperatures of -31°F: "I take my walk every day . in circles, ten times, twenty times, over the uneven snow drifts that have frozen as hard as steel." Walking to Lhasa in 1924, the explorer Alexandra David-Néel (who famously mastered the ancient meditative practice of thumo reskiang to self-heat) was stunned into enthralled silence by "the immensity of snow . an everlasting immaculate whiteness." Later, having trudged through miles of knee-high snow, she pronounced it "paradise.

" And yet for many of us, winter is the time we chose not to walk, preferring to stay home in the warm and dry. Big mistake! Decades after Carter, Ritter, and David-Néel embraced the cold, scientists are finally disentangling the extraordinary changes that take place in our bodies and brains when we spend time in moderate cold. Of course, ice, snow, and cold have been used to heal for centuries: Egyptian manuscripts refer to the use of cold water for reducing inflammation, British monks used ice as a form of anesthetic, and a nineteenth-century English physician called James Arnott used salt and crushed ice to reduce the pain of headaches and cancerous tumors. Fast-forward to Japan in the year 2000, and one of the first modern experiments to hint at the complexities of cold. Researchers identified two groups of female walkers: one group wore long skirts, covering every inch of leg, and the other group wore miniskirts, exposing their legs from ankle to thigh. The women agreed to wear the same skirts for a year and to have their legs regularly scanned. At the end of winter, magnetic resonance imaging (MRI) scans revealed that the legs of the miniskirted women had acquired an extra layer of fat. The legs of the long-skirted women, however, remained unchanged.

This doesn''t mean that exposure to cold makes us fat. Quite the reverse-as scientists were about to uncover. At the time it was thought that only hibernating mammals and babies carried a protective wrapping of brown fat, despite emerging studies implying that a few adults (outdoor workers in Scandinavia, for example) might also have pockets of it secreted beneath their skin. It was to be another decade before American researchers discovered the remarkable truth about brown fat-sometimes called brown adipose tissue (BAT)-the cold-induced fat acquired by the Japanese miniskirt wearers. In spite of its unfortunate name, brown fat is entirely free of the harmful lipids associated with excessive white or yellow fat. In fact, brown fat is a more effective fat burner than anything else, including muscle tissue, which might explain why thin, active people often carry more brown fat than their larger, more sedentary counterparts. But the most dramatic discovery came when researchers analyzed brown fat and found it packed with mitochondria, the tiny factories inside our cells that convert the food we eat and the oxygen we breathe into a form of energy called adenosine triphosphate (ATP). ATP supports every cellular process in our body.

Brown fat exists to keep us warm and breathing (alive), which explains why a flash of cold spurs it into life-increasing our metabolism, regulating our appetite, improving our insulin sensitivity, halting the premature death of our cells. Brown fat achieves this by producing molecules called batokines, which help preserve us in multiple ways. For example, batokines appear to stimulate production of follistatin, a protein that strengthens our muscles. Batokines also increase a compound called IGF-1, which encourages growth in every cell we have, meaning (very simply) that our bodies are better able to repair themselves, and hinting at why a 2021 study found people with good stocks of brown fat were also less likely to suffer from hypertension, congestive heart failure, and coronary artery disease. No wonder scientists are hopping with excitement at the therapeutic possibilities of brown fat. Not only does brisk walking in cold weather keep our cells healthy and our bodies in trim, muscular shape, it also keeps our brains in good working order. Studies suggest that we think more clearly in cold weather than in hot weather. Our brains run on glucose, and when glucose is low, our brains become sluggish.

We use more glucose cooling down than we use warming up, which could explain why some of us feel brain-foggy in hot climates but zingily alert in cold climates. A 2017 study from Stanford University found that people thought more decisively, calmly, and rationally in lower temperatures than in higher temperatures, reflecting a 2012 study that found warm weather not only impaired people''s ability to make complex decisions but made them more reluctant to engage with the decision in the first place. We don''t need to feel cold to experience enhanced cognition: merely looking at "cold" pictures makes our brains work with greater rigor. When Israeli researchers gave people a series of cognition tests interspersed with background images of either wintry, summery, or neutral landscapes, the participants achieved their best scores when they had the wintry images in their peripheral vision. Cold, in moderation, is also good for our mental health. A study of Polish students found that fifteen minutes in a chilly, leafless forest had "substantial emotional, restorative and revitalizing effects," implying that nature can make us feel just as rejuvenated in bare winter as in green-gold spring. Finally, a spot of cold appears to reduce feelings of stress. A 2018 report from the University of Luxembourg found that repeatedly applying cold to the necks of volunteers activated their parasympathetic (calming) nervous system, slowing and steadying heart rates-and raising the possibility that a judicious dose of chill could be more calming than one might think.

None of this is to suggest we purposefully make ourselves cold and miserable. Instead, we should welcome the colder months as an exhilarating time to walk. The views are altered: who doesn''t love the new vistas through sculpturally skeletal trees? Or the monochrome geometry of lines and shapes? Birdlife is more readily visible. Our brains are sharper, more zestily alert. Our beneficial brown fat is urged into action. To top it all, we build endurance: in lower temperatures, our hearts don''t have to work so hard and we sweat less, meaning our bodies work more efficiently. Tips How cold does it have to be? Not particularly . Brown fat is activated in mild cold, around 61°F, according to Dutch physiologist and brown fat researcher Wouter van Marken Lichtenbelt.

How long should we walk for? As long as suits, but one study found that two hours of exposure to moderate cold triggered the conversion of (bad) white fat (particularly in our stomachs and thighs) into (good) brown fat. Hate the cold? Numerous studies show that cold becomes less intimidating and discomforting the more we expose ourselves to it-a process called habituation. Wrap up warmly and increase the length of your walks bit by bit. Worried that cold air exacerbates allergies and asthma? A growing body of evidence suggests that winter exercise may do quite the reverse, reducing allergic inflammation in the airways and improving respiratory symptoms in many adult cases. Wear layers, so that you''re neither too hot nor too cold. Hands, feet, and head are often the first to cool, as blood floods to our vital organs to keep them warm, so wear fleece-lined gloves, thick socks, and a hat. If you''re warm enough, expose your forearms for vitamin D and your neck to activate brown fat (which often lies under the skin of the neck and collarbones, according to Ronald Kahn, professor of medicine at Harvard Medical School). Take a flask of something hot.

We often get unknowingly dehydrated in cold weather. A flask of coffee will help activate our brown fat: caffeine, like exercise and cold weather, is thought to spur brown-fat production. Walking in deep snow can be exhausting, so consider snowshoeing-an excellent way to walk long distances through snow. Worried about slipping on ice? Ensure your footwear has the best possible grip/traction (check sites like ratemytreads.com). Walk slowly and sideways on steps and downhill. Use walking poles. Our arms help us balance and our hands can prevent falls, so keep your gloved hands out of your pockets.

The cold is not a panacea, and hypothermia can kill, so wear the right clothes and footwear and walk as energetically as you can (see Week 2: Improve Your Gait, p. 10). Week 2 ImproveYour Gait when a youthful admirer told the French philosopher Simone de Beauvoir that he liked the way she walked, it was a compliment she never forgot. How we walk-our gait-provides a window into who and how we are. After Canadian researchers observed 500 walkers, they were able to identify (with an impressive 70 percent accuracy rate) which walkers had early cognitive impairment, reflecting previous studies suggesting that our gait.